Pointless comparison warnings

[federico-busato]

The fix addresses the following errors/warnings in fmt-9.0.0 with MICROSOFT MSC 191125506/GCC-7.5.0

\fmt/chrono.h(1399): warning #186-D: pointless comparison of unsigned integer with zero
          detected during:
            instantiation of "Int fmt::v9::detail::to_nonnegative_int(T, Int) [with T=unsigned long long, Int=long long, <unnamed>=0]" 
(1688): here

fmt/chrono.h(206): warning #186-D: pointless comparison of unsigned integer with zero
          detected during:
            instantiation of "To fmt::v9::safe_duration_cast::safe_duration_cast<To,FromRep,FromPeriod,<unnamed>,<unnamed>>(std::chrono::duration<FromRep, FromPeriod>, int &) [with To=std::chrono::duration<unsigned long long, std::ratio<1LL, 1LL>>, FromRep=unsigned long long, FromPeriod=std::micro, <unnamed>=0, <unnamed>=0]" 
(1436): here

fmt/core.h(408): warning #186-D: pointless comparison of unsigned integer with zero
          detected during:
            instantiation of "auto fmt::v9::detail::to_unsigned(Int)->std::make_unsigned<Int>::type [with Int=size_t]"
fmt/include/fmt/format.h(555): here

[vitaut]

Thanks for the PR. Could you provide a godbolt repro that triggers these warnings?

[federico-busato]

I realized that the warning is reproducible only with nvcc (Nvidia Compiler) independently from the host compiler (GCC, mvsc, etc.). Unfortunately, fmt is not available on godbolt with CUDA C++.
Just to show an example, considering https://github.com/fmtlib/fmt/blob/master/include/fmt/core.h#L408, this is the full log

fmt/include/fmt/core.h(408): warning #186-D: pointless comparison of unsigned integer with zero
          detected during:
            instantiation of "auto fmt::v9::detail::to_unsigned(Int)->std::make_unsigned<Int>::type [with Int=size_t]"
fmt/include/fmt/format.h(555): here
            instantiation of "auto fmt::v9::detail::fill_n(T *, Size, char)->T * [with T=char, Size=size_t]"
fmt/include/fmt/format.h(824): here
            instantiation of "fmt::v9::basic_memory_buffer<T, SIZE, Allocator>::basic_memory_buffer(const Allocator &) [with T=char, SIZE=500UL, Allocator=std::allocator<char>]"
fmt/include/fmt/printf.h(562): here
            instantiation of "auto fmt::v9::vsprintf(const S &, fmt::v9::basic_format_args<fmt::v9::basic_printf_context_t<fmt::v9::type_identity_t<Char>>>)->std::__cxx11::basic_string<Char, std::char_traits<Char>, std::allocator<Char>> [with S=fmt::v9::basic_string_view<char>, Char=char]"
fmt/include/fmt/printf.h(581): here
            instantiation of "auto fmt::v9::sprintf(const S &, const T &...)->std::__cxx11::basic_string<Char, std::char_traits<Char>, std::allocator<Char>> [with S=const char *, T=<int>, Char=char]"

and this is the code that triggers the error:

const int v = my_value;
fmt::sprintf("my_file", v);

[vitaut]

Is this warning enabled by default in nvcc?

[federico-busato]

yes, it is enabled by default (checked with nvcc CUDA 11.6)

[vitaut]

Merged, thanks.